/Engine/Plugins/Media/MediaIOFramework/Source/MediaIOCore/Public/MediaCapture.h
The capture is done on the Render Thread but triggered from the Game Thread.
virtual [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FMediaCaptureUserData](API\Plugins\MediaIOCore\FMediaCaptureUserData), ESPMode::ThreadSafe > GetCaptureFrameUserData_GameThread()